The present invention relates to a method for treating a substrate with heat sensitive agents. More particularly, the invention relates to a method of treating a substrate, e.g., by removing materials from the substrate surface, as in stripping, cleaning, etching and the like or by the addition of material, as by oxidizing the substrate surface, by contacting the substrate surface with both a heated liquid and a separate processing liquid comprising a heat sensitive agent. By utilizing a separate heated liquid to heat the substrate, rather than heating the processing liquid itself, the heat sensitive agent in the processing liquid is not detrimentally affected, and thus, enhanced treatment of the substrate can be achieved.
Ozone has long been recognized as a useful chemical commodity valued particularly for its outstanding oxidative activity. In fact, ozone is the fourth strongest oxidizing chemical known, having an oxidation potential of 2.07 volts. Because of this property, ozone and/or fluid mixtures including ozone are capable of removing a wide variety of contaminants, such as cyanides, phenols, and detergents, from surfaces. Also, ozone and/or fluid mixtures including ozone are capable of oxidizing surfaces.
Because of this wide range of activity, ozone finds application in many diverse processes. For example, ozone is useful for inhibiting, reducing and/or eliminating the accumulation of biomass, mold, mildew, algae, fungi, bacterial growth and scale deposits in various aqueous solution systems. As a result, ozone has been used as a biocide for the treatment of drinking water, as well as a sterilization agent in the brewing industry. When used in these applications, ozonation provides the advantage of producing a lesser quantity of potentially harmful residues than, e.g., chlorination, which leaves undesirable chlorinated residues in aqueous systems.
Ozonated water also finds wide utility in the semiconductor industry, where for example, ozone is used to xe2x80x9ccleanxe2x80x9d, i.e., oxidize, and surface condition the surface of in-process silicon wafers. Additionally, as is described in U.S. Pat. No. 5,378,317, ozonated water is used to remove organic materials, such as photoresist, from the surface of silicon wafers. Moreover, ozonated water may also be used to form a thin, passivating oxide layer on the surface of silicon wafers.
The use of ozonated water provides several advantages in these applications. First of all, because ozonated water is generated at the point of use, it is free of contaminants, i.e., particles and metals, that are typically present in chemicals that are stored in barrels or drums. Ozonated water is also less expensive than other oxidizing chemicals and furthermore, since ozonated water naturally decomposes, the use of ozonated water presents no disposal issues.
However, while ozonated water provides significant processing advantages, the effectiveness of ozone in each of these applications can be adversely affected by its low solubility and short-half life (approximately 10 minutes) in aqueous solutions. That is, not only is it difficult to dissolve ozone in an aqueous solution, but also, once dissolved, it is difficult to maintain the ozone in solution. Furthermore, the difficulties of achieving and maintaining a desired concentration of ozone in solution can be exacerbated in certain applications by the utilization or optimization of other processing parameters, such as pressure, flow rate and temperature, that can have an adverse affect on the solubility of ozone.
For example, in certain applications, such as the stripping of certain types of photoresist materials, it would be desirable to add heat to the processing system in order to accelerate the reaction kinetics and thus provide a faster rate of stripping of the photoresist material. However, heating a processing liquid comprising ozone may have the effect of undesirably diminishing the concentration of ozone in solution inasmuch as the increased temperature may cause an amount of ozone to effervesce out of solution. If too much ozone effervesces out of solution, the processing liquid solution may exhibit reduced stripping effectiveness. As a result, the enhanced rate of stripping that could otherwise desirably be achieved via the application of heat may be attenuated, negated, or the rate of stripping may even be reduced below the unenhanced rate, by the reduced stripping effectiveness of the ozonated solution.
Thus, it would be desirably to identify a method of treating substrates utilizing one or more processing liquids comprising heat sensitive agents such as ozone in which the temperature of the process could be optimized to realize enhanced treatment effectiveness, without detrimentally affecting the effectiveness of processing liquids.
According to the present invention, the above objectives and other objectives apparent to those skilled in the art upon reading this disclosure are attained by the present invention which is drawn to a method for treating a substrate. More specifically, it is an object of the present invention to provide a method wherein certain processing parameters that may otherwise have a detrimental affect on the effectiveness of the processing liquid(s) utilized in the method, such as the application of heat, may be utilized and/or optimized to achieve an enhanced treatment rate while not producing the predicted reduction in effectiveness of the processing liquid.
In particular, it has now been discovered that treatments involving heat sensitive agents may be carried out more effectively at higher temperatures by causing both a processing liquid comprising one or more heat sensitive agent(s) and a separate heated liquid to contact a substrate to be desirably treated with the processing liquid. Because the substrate is heated by the heated liquid, and further because the processing fluid is not substantially directly or indirectly heated for a long enough period of time prior to treatment, the effectiveness of the processing liquid is not substantially reduced. Thus, the method of the present invention provides a means of realizing the benefits that accompany the application of heat to a processing system, i.e., increased reaction kinetics, while also utilizing a processing liquid comprising a heat sensitive agent without a corresponding undue reduction in effectiveness of the processing liquid. In this manner, the method of the present invention is capable of producing enhanced treatment rates of substrates.
Thus, in one aspect, the present invention provides a method for treating a substrate. Generally, the method involves causing a heated liquid to contact the substrate in a manner effective to heat at least a portion of the substrate and causing a processing liquid comprising a heat sensitive agent dispersed and/or dissolved in a solvent to contact the heated substrate. Because the substrate is heated, an enhanced treatment rate of the substrate can be achieved. Furthermore, because the processing liquid is not substantially directly or indirectly heated for a long enough period of time prior to treatment, the effectiveness of the processing liquid is not substantially diminished, thereby further adding to the treatment effectiveness.
Advantageously, the method of the present invention is capable of heating a substrate, or plurality of substrates, substantially uniformly. As a result, the method of the present invention has proven to be particularly useful when utilized in spray processing systems to process a plurality of substrates such as semiconductor wafers. Therefore, in another aspect, the present invention provides a method of treating a plurality of substrates. In particular, the method involves positioning the plurality of substrates in a chamber and causing a spray of a heated liquid and a spray of a processing liquid comprising a heat sensitive agent to contact the plurality of substrates. Again, because the heat is brought to the treatment by the heated liquid, the rate of treatment is enhanced over that achieved when no heat is applied. Furthermore, because the processing liquid itself is not heated to a sufficient degree for a long enough period of time prior to treatment, the effectiveness of the processing liquid is not substantially diminished thus further contributing to the enhanced treatment rate.
As used herein, the term xe2x80x9cozonatedxe2x80x9d means that ozone is dispersed and/or dissolved in a given solvent. The phrase xe2x80x9cultrapure deionized waterxe2x80x9d, as used herein, is meant to indicate water that has been treated by, for example, filtering, reverse osmosis, and/or UV sterilization so as to remove particles, metals and organic materials, respectively. Also, as used herein, the phrase xe2x80x9cheat sensitive agentxe2x80x9d means an agent whose physical or chemical properties are altered by a change in temperature. One example of a heat sensitive agent is ozone, the solubility of which typically decreases with an increase in temperature.